1. Field of the Invention
The present invention relates to a user interface technique that enables iteration in visual programming and, more particularly, but not by way of limitation, to iterator link objects.
2. Description of the Related Art
The user interfaces of existing visual programming products allow users to visually create simple event-action sequences. For example, some visual programming products allow the user to visually "link" a source object, such as a pushbutton or data file, to a target object, such as a database or entry field. The link recognizes specific "events" of the source object, such as click, press, release, double click, etc., or specific states of the source object. When the event occurs, the link sends a message to the target object. The target object then performs specific data processing (e.g., delete, insert, clear, append, etc.) in accordance with the received message. As such, the contents of the link are referred to as an event-message pair. The event-message pair identifies the source object, source event, target object, and target action. Illustratively, using a visual builder screen, a user can link a pushbutton icon to an entry field icon so that when the user clicks the pushbutton icon with the pointer of a mouse, the entry field clears.
Links may be implemented as objects. Link objects provide the user with common object behaviors and, thus, can be manipulated like other objects. For example, link objects can be created from link template icons, copied to a clipboard and pasted elsewhere, dragged to a trashcan and deleted, and opened to display their properties. Consequently, link objects help provide a user, particularly a novice user, with a visual programming environment for developing application programs.
Conventionally, link object graphics have three components. Two of the components are link handles and one component is a link connector. A user moves (e.g. drags) each handle across the display screen with the assistance of a pointer and a pointing device, such as a mouse, and places (e.g. drops) each handle over another object. The link connector continuously follows the pointer during direct user manipulation and then appears between the two link handles when the link is established. If desired, the resulting link object's event/message pair can be modified by opening the link object to display its properties.
Conventional link objects, however, suffer significant limitations and disadvantages when the user desires to build more sophisticated applications. Illustratively, a user may often desire to insert a multiple element source object, such as an array of fifty names, into a target object, such as a database. Therefore, the link object must be capable of repeating (i.e., iterating) the insert action for each element of the array. Further, the user may desire to insert the array of names into several databases.
To create these applications using current tools, the user must utilize a suitable programming language, such as BASIC, Smalltalk, or C++, to program the iteration of these applications. Unfortunately, users are often unfamiliar with these programming languages and, therefore, cannot build applications that use iteration. Therefore, because many applications require iteration, a great demand exists for a visual representation of iteration. Such a representation would allow non-programmers to create iterative applications without having to learn a programming language.